1. Field of the Invention
The present invention relates to a cartridge case that includes a first case provided with a positioning reference hole and a second case and is constructed so as to house an information recording carrier, and to an information recording medium where an information recording carrier is included inside such cartridge case.
2. Description of the Related Art
As one example of an information recording medium where an information recording carrier is housed inside a cartridge case, Japanese Laid-Open Patent Publication No. 2001-195864 discloses a magnetic tape cartridge (hereafter, simply “tape cartridge”). The tape cartridge is constructed with a reel, around which magnetic tape (an information recording carrier) is wound, rotatably housed inside a cartridge case that includes a lower case (first case) and an upper case (second case). When the tape cartridge is loaded in a recording/reproducing apparatus, the magnetic tape is pulled out of the cartridge case and subjected to recording and reproducing. Reference holes for positioning the cartridge case at a predetermined recording/reproducing position in the recording/reproducing apparatus are formed in a baseplate of the lower case. During the recording/reproducing process, in a state where positioning pins are inserted into the reference holes to position the cartridge case at a recording/reproducing position inside the recording/reproducing apparatus, the magnetic tape is pulled out from the cartridge case and the magnetic tape is wound back from inside the cartridge case.
On the other hand, by investigating the tape cartridge (cartridge case) described above, the present inventor discovered the following problem. That is, with this type of tape cartridge, the reference holes are formed in the cartridge case so that when the cartridge case is loaded into a recording/reproducing apparatus during the recording/reproducing process, positioning pins are inserted into the reference holes after the cartridge case has been conveyed to the recording/reproducing position by a loading mechanism. At this time, as shown in FIG. 5, due to extremely small displacements of the cartridge case 2x (in the following description, component elements of the conventional tape cartridge are indicated by attaching “x” to the reference numerals) relative to the loading mechanism (not shown), a front end portion of a positioning pin Px may contact and catch on a rim portion of a reference hole 27x as shown by the broken line in FIG. 5. As this type of tape cartridge is easy to mold and resistant to thermal deformation and the like, the cartridge case 2x(the upper case and lower case 2bx) is injection molded using polycarbonate, for example. This means it is difficult for the positioning pins Px to slide on the cartridge case 2x. 
Accordingly, when the tape cartridge is used repeatedly, there is the problem of damage being caused to the rim portions of the reference holes 27x(i.e., the surface of the baseplate 2cx) of the lower case 2bx due to the positioning pins Px catching thereon. If the positioning pins Px catch on the surface, the loading mechanism repeatedly carries out the conveying process (loading process) for the cartridge case 2x until the positioning pins Px are properly inserted into the reference holes 27x. As a result, there is a problem of a long time being required from the loading of the tape cartridge into the recording/reproducing apparatus until the start of the recording/reproducing process. Also, the recording/reproducing apparatus described above is constructed so that when the number of repeated executions of the loading process reaches a predetermined number, it is determined that a “loading error” has occurred and the recording/reproducing process on the tape cartridge is suspended. Accordingly, when a backup process for recording data is carried out on a data server using a tape cartridge as a backup medium, for example, there is the risk of a major accident where the occurrence of a loading error prevents the backup process from starting at a predetermined time.
On the other hand, when the entire cartridge case 2x (the lower case 2bx) is made of a metal material, for example, to avoid damage to the rim portions of the reference holes 27x of the lower case 2bx, there is the problem of a large increase in the manufacturing cost. To prevent loading errors from occurring, the entire cartridge case 2x (the lower case 2bx) may be molded using various types of resin materials on which the positioning pins Px can slide favorably when the positioning pins Px contact the reference holes 27x, but doing so carries the risk of a fall in strength and also of thermal deformation of the cartridge case 2x (the lower case 2bx) when the cartridge case is exposed to high temperatures inside the recording/reproducing apparatus or the like.